Electrolytic process for preparing manganese and manganese dioxide simultaneously



T. A. MnTcHELL ET A1. 2,417,259 ELECTROLYTIC PROCESS FOR PREPARING MANGANESE March l1, 1947.

AND MANGANESE ADIOXIDE SIMULTANEOUSLY Filed April 15, 1942 INVENTOR5 ma@ @EZ UNITED STATES PATENT OFFICE ELECTROLYTIC PROCESS FOR PREPARING MANGANESE AND MANGANESE DIOXIDE SIIVIULTANEOUSLY Thomas Austin Mitchell and Donald Cooper Mitchell, Torrance, Calif., assignors to American Manganese Corporation, Dover, Del., a corporation of Delaware Application April 15, 1942, serial No. 439,038

s claims. (C1. zoll- 96) The invention relates to a process for the Winning of manganese. tains to the deposition of metallic maganese and formation of manganese dioxide and includes cor- More particularly, it per-' 2 the electrolytes in separate compartments, these compartments being set up through utilization of a diaphragm of slight porosity.

A principal feature of the procedure resides in` related improvements and discoveries whereby 5 the simultaneous and continuous electrolysis of their production may be enhanced. two different electrolytes, one on each side of a An object of the invention is to provide a procporous diaphragm. As above indicated, the ess whereby metallic manganese and manganese catholyte liquor contains manganese sulfate and dioxide are simultaneously formed. ammonium sulfate and, in addition thereto, there A further object of the invention is the prol0 may be a content of free ammonia and this elecvision of a process in accordance with which trolyte is continuously electrolyzed to form metallic manganese is deposited in a catholyte metallic. manganese. The presence of free amand manganese dioxide simultaneously formed in monia leads to a reaction thereof With sulfate ions an anolyte of differing compositions. to form ammonium sulfate. A factor in the pro- An additional object is to provide a process for cedure is the maintenance of an excess of free the winning of manganese and formation of ammonia in the catholyte. A continuous flow of manganese dioxide in which constancy of action catholyte through a catholyte chamber of the and of concentration of catholyte and of anolyte electrolytic apparatus is occasioned through cirare maintained. culation, and there is also a separate circulation Another object of the invention is to provide and hence continuous feed of the anolyte to, a process for the simultaneous deposition of through and from-an anolyte chamber. The anomanganese and formation of manganese dioxide lyte is an acidiiied manganese sulfate solution of which may be readily, effectively and economknown strength containing sulfuric acid, and the ically carried out to a desired commercial exelectrolysis results in a continuous formation 0f tent. manganese dioxide with production of sulfuric A still further object of the invention is the acid taking place at the same time. provision of a process whereby metallic manga- As a result of the formation of manganese nese is deposited and manganese dioxide formed dioxide the manganese sulfate concentration is under the iniiuence of an electric current with decreased, whereas that of the sulfuric acid incontinuous formation and removal of manganese creases and reaches a value at which it is desirdioxide. able to circulate the electrolyte through the ano- A more particular object of the invention is to lyte chamber, and by so doing formed mangaprovide a procedure which entails retention of nese dioxide in suspension is continuously remanganese values in a catholyte and in an anomoved. The diaphragm which sets up independlyte by separate contacting thereof with a mass ent anolyte and catholyte chambers in the eleccontaining manganous oxide, as a reduced mantrolytc apparatus is of a slightly porous maganese ore. terial, which may be ceramic, and it acts mainly Other objects of the invention will in part be as a carrier of the electric current between the obvious and will in part appear hereinafter. anode and the cathode and does not permit any The'invention accordingly comprises the sev- 40 marked migration of sulfuric acid or of sulfate eral steps and the relation of one or more of ions from the cathode to the anode chamber. such steps with respect to each of the others This has been demonstrated in practice inasmuch thereof, which will be exemplified in the process as the amount of free ammonia required toA mainhereinafter disclosed, and the scope of the in- I tain the desired concentration in the catholyte is vention will be indicated in the claims. f5 directly proportional to the amount of manga- In the practice of the invention a deposition nese deposited. Moreover, the amount of mangaof metallic manganese and simultaneous formanese'dioxide formed in the anolyte is directly tion of manganese dioxide is effected under the proportional to the amount of sulfuric acid proinfluence of an electric current. The manganese duced therein. j l is produced on a cathode from an alkaline catho- A carrying vout of the procedure brings about lyte containing manganese sulfate and amthe simultaneous production of pure metallic monium sulfate, and formation of manganese manganese and high grade manganese dioxide dioxide is brought about at an anode in an anoin amounts which occasion an appreciable reduclyte containing manganese sulfate and sulfuric tion in power cost, especially with respect to acid. The cathode and anode are immersed in deposition of manganese metal. Effective operation of the process requires one kind of electrolyte about the cathode and another about the anode, with separation thereof by, desirably, a ceramic diaphragm which may constitute a rectangular vessel or tank containing the catholyte with the cathode immersed therein. The electrolytic apparatus or cell can be operated with a number of diaphragms, for example, up to 10, and the space about them is occupied by the anolyte in which the anodes are immersed, Ithen being one more anode than cathode. A separate continuous iiow or circulation of catholyte and anolyte may be maintained through vthe cell in order to retain the proper concentration of manganese between the electrodes, and .more particularly with respect to the anode in order to remove the manganese dioxide produced. The catholyte, by suitable means, may be distributed tothe various cathode chambers and recollected or reassembled as it flows from them. A like arrangement may ,bey utilized for introduction .and removal of the anolyte from the .anode chambers or spaces.

A suitable construction is to form the bottom of the .cell as a .hopper which receives the manlganese dioxide dropping from the anodes. A discharge pipe may lead from the hopper and terminate at a .point directly outside of the cell but slightly below the level of the anolyte. Thereby anolyte .containing suspended Loxide is withdrawn and the oxide may be recovered in settling tanks. Amore rapid `circulation `of anolyte is set up than of catholyte Ain order to insure removal of the .manganese dioxide. The catholyte initially may contain about 'l5 grams manganese sulfate and about 200 grams of ammonium sulfate per liter,

and .this maybe .circulated vthrough the cell until ,the manganese sulfate content has decreased to from 50 to 60 grams per liter. During this period the ammonium .sulfate concentration is increased .to about .220 grams ,p er'liter because of the addivtion .of ammonia to the catholyte prior to its enrtrance Yinto the `cell .or reaction zone.

Vmonia which is given off as `gas and utilized throughintroductioninto the `catholyte as it flows back to the cell.

.It .is 4desirable that the catholyte be puried subsequent to Vits contact with the reduced ore .and prior to its .flowing into the cell inasmuch as small .amounts of various elements, as iron, arsenic, nickel, cobalt, copper, etc. have been taken up and which interfere with the electrolytic action. One `mode of `.operation entails contactying only a part of the spent catholyte with the ,reduced ore, with obtainment of a Vliquor containing B Vgrams of manganese sulfate per liter. liquor .also contains unreacted ammonium sulfate Yand may be admixed with .another or remaining fraction of spent catholyte to prepare `a fresh batch .of catholyte liquor for introduction into the cell and which would contain about 80 .grams manganese sulfate and 200 grams ammo- .nium .sulfate per liter. The anolyte initially may contain about 150 grams manganese sulfate and about 75 .grams sulfuric acid per liter, and this may be circulated .through the cell until the sulfuric acid lcontent has increased to about 90 .4 grams. A portion of the anolyte liquor is then treated with a reduced manganese ore for reduction in sulfuric acid concentration through reaction with manganous oxide. Thereby the manganese sulfate concentration may be increased to about .300 grams or more per liter, and accomplishment of this may require addition of some concentrated sulfuric acid to the anolyte liquor.

As in the case of the catholyte a purification of the anolyte liquor may be carried out in order to iremove those metals, as iron, arsenic, etc., which are vdissolved from the reduced ore. Removal of deposited manganese, from the cathodes may be carried out about every three days, oras may be considered necessary by withdrawing the cathodes .from `the .electrolyte and stripping the deposited metal therefrom with clean electrodes being substitutedfor those withdrawn.

More particularly, the practice of the invention follows the ow sheet illustrated in the drawing, in which the various steps are shown and indicated Vby appropriate legends. The procedure involves the simultaneous deposition of manganese dioxide with maintenance of two separate and distinct electrolyte systems, one an anolyte system in which manganese dioxide is formed, and the other .a catholyte system in which manganese metal is produced. An electrolytic cell makes up Vthe principal Vreaction zone and is composed of two separate sections, one of which may be situated `within the other, with yformation of two concentric compartments separated by inner section walls which constitute a diaphragm and may be 'a slightly porous ceramic-like cup or cell. The cathode or cathodes, e. g. of stainless steel, are suspended within the cup or diaphragm, andthe anodes Vwhich preferably Aare sheets of lead outside. With a proper regulation of temperature Yand current density we have found that the anodes are vself-cleaning through a constant dropping oif of the formed 4manganese dioxide, whereas `the cathodes are removed and replaced at Asuitable intervals depending upon the current density and thickness of the deposit of manganese metal. 'Following stripping of the metal from the cathodes they are again prepared foruse and at a `suitable time placed within the'cells. The process may be carried out with an over-all cell temperature from about 20 to about 30 C., and at a current density which may range from about 18 vto 30 amperes per square foot on both anode and cathode.

The Yanolyte being circulated may have a concentration from about to about 200 grams of manganese sulfate and from about 50 to 100 grams of sulfuric acid per liter.l A flushing out of the oxide is accomplished by circulation of the anolyte and following settling by a suitable means the clarified liquor is returned to the reaction zone. If desired, a part of the anolyte may be removed from the system, .either periodically or continuously, 4with an addition at the same time of fresh manganese sulfate liquor, eitherV neutral or v'along with some of the spent anolyte. Thereby sulfuric acid which is formed simultaneously with the manganese dioxide is removed, and the cell replenished with-manganese sulfate. It is probable that manganese dioxide is formed at the an.. ode in yaccordance with the following equation:

The oxygen called for .arises at the anode due to electrolysis of water. `In .the catholyte the concentrations of manganese sulfate and ammonium .sulfate are sufciently low toobviate crystal forforming manganese sulfate and Water.

Jentry into the cell.

`mation at the operating temperature, and the solution initially may contain about 75 grams manganese sulfate, 200 grams ammonium sulfate and from about to about l0 grams free ammonia per liter. We have found that a small amount of Vsulfur dioxide serves to inhibit oxidation of manganous hydroxide in suspension, and this amount may be from about 0.2 to 0.5 grams per liter. The spent catholyte owing from the cell contains about 50 grams manganese sulfate, 220 grams ammonium sulfate and 2 grams free ammonia per liter. An amount of free ammonia is reacted 'during the electrolysis, which corresponds substantially to the following reaction:

MnSO4-l-2NH3-l-2H=Mn+ (NH4) 2SC-i Hydrogen arises from the electrolysis of water and the catholyte circuit is considered to be an ammonium sulfate-ammonia cycle, inasmuch as ammonia is recovered from ammonium sulfate during contact with a reduced manganese ore, vand this ammonia reused through introduction into the catholyte prior to its entrance into the reaction zone.

Two separate and distinct reduced ore contacting and purification circuits are employed, with the catholyte system recovering ammonia. The anolyte leach or ore treatment is a neutralization of sulfuric acid by means of manganous oxide A purification of the anolyte liquor may be accomplished through oxidation with respect to iron and arsenic, chlorine removal by means of a "soluble silver salt, hydrogen sulfide treatment at a pH value of 5.5 with heating to 7 0 to 80 C. if

'desired and, iinally, removal of excess hydrogen sulfide. When so purified the anolyte liquor is in condition for introduction into the cell or reaction zone. y

Treatment of the reduced ore with the circulating catholyte is somewhat more involved than that of the anolyte, inasmuch as it is accompanied by a simultaneous and continuous recovery of amomnia. The reaction with manganous oxide is believed to take place according .to the following equation:

'A slightly reduced pressure on the leaching system assists in the removal of the ammonia which is formed and the ammonium sulfate is not entirely replaced by manganese sulfate inasmuch as it is desired to produce as nearly as possible a liquor of proper composition for introduction into the cell. Purification of the liquor comprises oxidation with air with respect to iron and arsenic and treatment with hydrogen sulfide or ammonium sulfide to remove small amounts of other metals, as cobalt and nickel, with removal of any excess sulfide by treatment with ammonia.

An adjustment of the final desired concentration may be effected through addition of some of `the catholyte coming from the cell, and an addition of sulfur dioxide gas may be made in an amount from about 0.2 to 0.5 grams per liter. Following this the catholyte is in readiness for the addition of ammonia, which is introduced just prior to the catholyte entering the cell. We have found it advisable to recirculate a portion of the catholyte over a period, for example, several hours, in order to decrease the manganese content, and when so doing the recirculated catholyte is treated with ammonia gas prior to re- The ammonia gas arising 6 from treatment of the reduced ore is a mixture of ammonia and water vapor. This water vapor may be condensed in a suitable heat exchanger and the free ammonia is conducted to ammonia addition units for introduction into the catholyte with attending pH control. The condensed water vapor contains ammonia, and this may be recovered by stripping with high pressure steam. If desired, a portion of the catholyte may constitute a medium for generation of ammonia through treatment with calcium hydroxide whereby ammonia gas is liberated and may be combined with that arising from the treatment of reduced ore.

A carrying out of the foregoing procedure results in .the simultaneous production of metallic manganese and manganese dioxide. The oxide, which is in. hydrated form, may be removed from the anolyte by means of a thickening settler, and the thickened oxide pulp filtered and washed to 'remove manganese sulfate and sulfuric acid.

This may be accomplished through employment of acid-proof continuous drum lters spaced by repulping steps. The washed oxide may be suitably dried and then classified and packed. Metallic manganese is deposited in a condition of high purity upon the cathodes, which are removed, dipped in a, dichromate bath, and washed with Water. The cathodes are then dried and the metal stripped therefrom. This may be packed as stripped from the eathOdeS, or it may be melted and cast.

The foregoing procedure is characterized by the features that an anolyte is maintained separate and distinctly different from a catholyte, and furthermore that there is no admixture of catholyte and anolyte at any time. It is one of our findings that the anolyte, being essentially an aqueous solution of manganese sulfate and sulfuric acid, should no-t contain any ammonium sulfate if a high current efficiency with respect to oxide formation is -to be obtained. Consequently, at no time is there a mixing of the anolyte with the catholyte. Additionally, a sulfuric acid cycle is maintained for the anolyte and an ammonium sulfate-ammonia cycle for the catholyte, and the cell or reaction zone is so designed that the oxide formed may be continuously and effectively removed. Moreover, a neutralization of sulfate ions set free by the deposition of metallic manganese with free ammonia is preferred, and there is thus set up an ammoniaammonium sulfate cycle in which ammonia is suitably regenerated and returnd .to the reaction zone.

A tight and slightly porous diaphragm is employed which we have found acts as a carrier for the current while effectively inhibiting passage of the solutions. This permits neutralization of sulfate ions in the catholyte circuit while keeping the two circuits separate. In practice we produce about two pounds of manganese dioxide for each pound of metallic manganese without any increase in current input. and this results in a decrease in the required kilowatt hours per pound of product. Furthermore, the metallic manganese produced has a purity of over 99% and the manganese dioxide simultaneously formed yis also of a high purity,

We have obtained an apparent efficiency' of about 50% in the production of metal and of about 30% in the production of manganese dioxide when all the kilowatt hours consumed are referred either to the metal or to the oxide. However, when the combined production of metal and oxide is referred to the manganese, then there is an attending eciency of about 80%. It will be observed that metal production and manganese dioxide formation, take place at the same time and from the same electrical current. We have obtained some results of about 50% current eiiiciency for the metal andabout 60% current eiiiciency for the oxide, which would mean 110%, as the same current produces both products. Moreover, the production of two pounds of manganese dioxide for each pound of manganese metal means that three pounds of product are obtained instead of one pound, as is the case when metal alone is produced.

Since certain changes may be made in carrying out the above process Without departing from Having described our invention what We claim as new and desire to secure by Letters Patent is:

1. A process for winning manganese and preparation of manganese dioxide which comprises electrolytically depositing metallic manganese on a cathode from an alkaline catholyte containing manganese and ammonium sulfates, and simultaneously electrolytically forming manganese dioxide at an anode in an anolyte containing man.. ganese sulfate and sulfuric acid the weight ratio of oxide to manganese being about two to one, said catholyte containing initially about 75 grams of manganese sulfate and about 200 grams of ammonium sulfate, from about to about 10 grams free ammonia and from about 0.2 to 0.5 gram sulfur dioxide per liter and said anolyte having a concentration during electrolysis from about 100 to about 200 grams of manganese Sulfate and from about 50 to 100 grams of sulfuric acid per liter, said catholyte and anolyte being circulated and maintained separate throughout the action.

2. A process for winning manganese and preparation of manganese dioxide which comprises electrolytically depositing metallic manganese on a cathode from an alkaline catholyte containing initially about 75 grams manganese sulfate, about 200 grams ammonium sulfate and from about 5 to about grams free ammonia per liter, and simultaneously electrolytically forming manganese dioxide at an anode in an anolyte having a concentration during electrolysis from about 100 to about 200 grams manganese sulfate and from about 50 to about 100 grams sulfuric acid per liter, the weight ratio of oxide to manganese being about two to one, said deposition and formation being effected at a temperature from about to about 32 C. and a current density from about 18 to about 30 amperes per`- square foot of anode andcathode surface, and circulating and maintaining catholyte and anolyte separately with contact with a reduced manganese ore.

3. A process for winning manganese and preparation of manganese dioxide which` comprises electrolytically depositing metallic manganese on a cathode from an alkaline ctaholyte containing initially about 75 grams manganese sulfate, about 200 grams ammonium sulfate and from about 5 to about 10 grams free ammonia per liter, and

. s i simultaneously electrolytically forming manganese dioxide at an anode in an anolyte having a concentrationduring electrolysis from about to about 200V grams manganese sulfate and from about 50 to about 100v grams sulfuric acid per liter, the weight ratio of oxide to manganese being about two to one, said deposition and formation being effected at a temperature from about 20 Vto about 32 C. and a current density from about 18 to about 30 amperes per square foot of anode and cathode surface, circulating and maintaining catholyte and anolyte separately Y with contact with a reduced manganese ore, and introducing ammonia into circulating catholyte prior to its entrance into the reaction zone.

4. A process for winning manganese and preparation of manganese dioxide which comprises electrolytically depositing metallic manganese on a cathode from an alkaline catholyte containing manganese and ammonium sulfates, simultaneously electrolytically forming manganese dioxide at an anode in an anolyte containing manganese. sulfate and sulfuric acid, the Weight ratio of oxide to manganese being about 2 to 1, and circulating and maintaining catholyte and anolyte in separate circuits with leaching of separate sources of material containing manganous oxide in each circuit,

5. A process for winning manganese and preparation of manganese dioxide which comprises electrolytically depositing metallic manganese on a cathode from an alkaline catholyte containing manganese and ammonium sulfates, ammonia, and suliite ions, and simultaneously elec-l trolytically forming manganese dioxide at an anode in an anolyte containing manganese sulfate and sulfuric acid, and circulating and maintaining catholyte and anolyte in separate circuits with leaching of separate sources of material containing manganous oxide in each circuit, the weight ratio of oxide to manganese being about 2 to 1.

6. A process for Winning manganese and preparation of manganese dioxide which comprises electrolytically depositing metallic manganese on a cathode from an alkaline catholyte containing manganese and ammonium sulfates, simultaneously electrolytically forming manganese dioxide at an anode in an anolyte containing manganese sulfate and sulfuric acid, the weight ratio of oxide to manganese being about 2 to 1, and circulating and maintaining catholyte and anolyte in separate circuits with leaching of separatesources of reduced manganese ore in each circuit.

'7. A process for winning manganese and preparation of manganese dioxide which comprises electrolytically depositing metallic manganese on a cathode from an alkaline catholyte containing manganese and ammonium sulfates, simultaneously electrolytically forming manganese dioxide at an anode in an anolyte containing manganese sulfate and sulfuric acid, the weight ratioy of oxide to manganese being about 2 to 1; said deposition and formation being effected at a temperature from about 20 to about 32 C. and at a current density from about 18 to about 30 amperes per square foot of anode and cathode surface, and circulating and maintaining catholyte and anolyte in separate circuits ywith leaching. of separate sources of material containing manganous oxide in each circuit.

8. A Yprocess for winning manganese and preparation of manganese dioxide which comprises electrolytically depositing metallic manganese on a cathode from an alkaline catholyte containing manganese and ammonium sulfate, simultaneously eectrolytically forming manganese dioxide at an anode in an anoyte containing manganese sulfate and sufurie` acid, the Weight ratio of oxide to manganese being about 2 to 1, circulating and maintaining catholyte ano. anolyte in separate circuits with leaching of separate sources of material containing manganello oxide in each circuit, and introducing ammonia and sulfur dioxide into circulating catholyte prior to its entrance into the reaction Zone.

THOMAS AUSTIN MITCHELL. DONALD COOPER MITCHELL.

10 REFERENCES CITED Y The following references are of record in the le of this patent:

5 UNITED STATES PATENTS Number Name Date 2,119,560 Shelton June 7, 1938 2,259,418 Hannay et a1 Oct. 14I 1941 2,286,148 Mantell June 9, 1942 10 2,361,143 Leute et a1 001.24, 1944 2,356,515 Guareschi Aug, 2,2, 1944 OTHER REFERENCES Bureau of Mines R. I., page 21, 3580, Sept. 1941. 15 Report of Inv. No, 3651, Bureau of Mines, July 

